1. Field of the Invention
The present invention relates to a vertebral osteosynthesis device that can be used to brace a spine, for example, following accidental fracture, or to strengthen or brace a deviated spine, as in the case scoliosis or kyphosis. More particularly, this invention is related to a novel cross connector which fixes the location and enhances the rigidity of longitudinally extending rods anchored to the spine.
2. Discussion of the Prior Art
As is known, from, for example, U.S. Pat. No. 5,055,562 to Cotrel, a pair of posterior rods may be coupled to the back of a spinal column by hooks held by screws supported by the pedicles of the vertebra. Generally, there are two rigid and substantially parallel support rods disposed one on each side of the spine supported by pedicle screws or hooks. These vertically aligned rods stabilize both short and long segments of the spine. Implantation of such a device requires the rods to be shaped to adapt to the curve in one or two planes of the spine, whether these are nature curves or curves resulting from scoliosis or kyphosis.
In order to provide enhanced rigidity, especially torsional rigidity, the pair of rods usually includes cross connecting devices which couple the rods together transverse to their longitudinal axis, i.e. transverse to an axis extending in the vertical direction when an individual is standing.
As can be seen from U.S. Pat. No. 5,005,562 these cross connector devices include a plurality hook shaped gripping elements which receive the rod. These elements are fixed to the rods by set screws which extend through a wall of the hook. Since the rods may be curved in the medial-lateral direction and the distance between the pair of rods may vary consequently, a method for varying the horizontal distance between the hooks is required. As can be seen in U.S. Pat. No. 5,002,562, one solution is to provide a threaded transverse rod on which the hooks may be threaded for movement therealong. Of course, this limits the adjustibility of the hooks, depending on the fineness of the thread and the required angular orientation necessary to engage the vertical rods.
Consequently, Cotrel, in his later U.S. Pat. Nos. 5,601,552 and 5,651,789 uses a transverse bar of polygonal shape which allows the hooks to slide and be fixed in any relative horizontal position along the bar. However, such a system exhibits only one degree of freedom since the hook surfaces always move in the same plane.
In U.S. Pat. No. 5,667,507 to Corin, et al., a cross locking member is provided, which includes an additional degree of freedom, allowing rotation in the vertical plane as well as length adjustment in the horizontal direction. Thus, two degrees of freedom are provided. Similarly, U.S. Pat. No. 5,752,955 provides two degrees of freedom by allowing rotation around a horizontally extending axis as well as allowing equalized extension via a telescoping connection between the hook bodies.
U.S. Pat. No. 5,443,465 to Pennig discloses a fracture fixation device having multiple degrees of freedom. However, this device requires several joints which have to be independently locked to fix the device in a given position.
U.S. Pat. No. 5,716,355 to Jackson, et al. relates to a pair of connectors slideable along each to two parallel spinal rods and having swivel connections to fix the final orientation of a transverse rod relative to the spinal rod. This design requires both connectors to be independently adjusted and locked to fix the transverse rod in its final position.
U.S. Pat. No. 5,261,907 to Vignaud, et al. relates to a cross connecting device having a pair of rods and a pair of clamps which can be fixed in place, utilizing a screw arrangements. This device is difficult to assemble because it includes two clamps, each receiving its own extension arm which arms are independently adjustable within the clamps.
None of the prior art discloses transverse cross connector having multiple degrees of freedom which cross connector can be locked in a desired position by a single locking mechanism.